Selective printing using electrostatic techniques



Nov. 23, 1965 c, o, c nREss 3,218,967

SELECTIVE PRINTING USING ELECTROSTATIC TECHNIQUES Filed Dec. 20, 1962 2 Sheets-Sheet 1 POWDER QESERVOI R I $DLENO\D A\R SELECTO R COM PRE $302 POWDER RESEFZVO "2.

CLYDE O. CH\LD\ZESS INVENTOR.

41B BY jm-wl ATTORNEY Nov. 23, 1965 c. o, CHILDRESS 3,218,957

SELECTIVE PRINTING USING ELECTROSTATIC TECHNIQUES Filed Dec. 20, 1962 2 Sheets-Sheet 2 RECJPROCAL ACTUATOR /-88 MOTOR i RECJPROCAL 5Q ACTUATOR MOTOR HG PHOTO- ELECTRK, DETEC'flNC-s APPARATUS REG PEOCA L ACTU ATO P. M OT0 l2 CLYDE O. CH\LDEES5 INVENTOR.

JM My,

ATTORNEY.

United States Patent SELECTIVE PRINTING USING ELECTRUSTATIC TECHNIQUES Clyde 0. Childress, Palo Alto, Calif., assignor to Electrostatic Printing Corporation of America, San Francisco,

Calif., a corporation of California Filed Dec. 20, 1962, Ser. No. 246,139 5 Claims. (Cl. 101-114) This invention relates to electrostatic printing systems and more particularly to improvements therein.

In an application for electrostatic printing by Clyde 0. Childress et al., Serial No. 12,714, filed March 4, 1960, subsequently issued as Patent No. 3,081,698, there is described an electrostatic printing process which effectively comprises transferring particles through an image forming electrode across an air gap in which an electric field has been established, to an image receiving electrode, or to paper which is inserted between the two electrodes. The two electrodes may be in the form of parallel conductive planes that 'are held at an electrical potential difference so that they define a substantially uniform electrostatic field.

The image electrode is a thin conductive member with printing areas composed of groupings of relatively small discontinuous openings. A preferred arrangement for the image electrode is a conductive screen in which all but the desired image areas are masked off. Printing is accomplished by bringing charged dry ink particles into the electrostatic field through the image defining openings. The particles are transported along lines of force perpendicular to the image plane, and reproduce the patterns of openings of the image electrode on the receiving electrode, or upon a sheet of paper or other material that has been interposed between the electrodes. The charged particles are firmly held to the surface upon which they are deposited by electrostatic attraction until the image is permanently fixed by heat, solvent vapor, or other means, depending upon the composition of the image particles.

In an attempted application of the foregoing process to on line :printing of data, or where printing on material having a high temperature, problems arise. By on line printing is meant, the type of printing that occurs with a typewriter, for example, or with high speed printing apparatus of the type employed to print the output of a computer. By materials having a high temperature is meant hot metal in the form of cans, or hot glass in the form of bottles, for example. It appears that in order to enable the dry ink powder particles to enter into the eletcrostatic field through the stencil screen, it is necessary to literally rub or force the powder through the screen mesh openings, using a brush or other means. Otherwise, despite the fact that the powder particle sizes are smaller than those of the openings in the screen, the powder does not pass freely and evenly through these openings. The use of a rotating brush with on line electrostatic printing equipment is extremely difficult, and clumsy, and with hot materials may be diflicult.

Accordingly, an object of this invention is the provision of on line electrostatic printing equipment which eliminates the need for brushing pigment particles against the screen openings.

Yet another object of the present invention is the provision of novel, and unique on line electrostatic printing apparatus.

Still another object of the present invention is the provision of an improved arrangement for effectuating electrostatic printing.

These and other objects of the present invention are achieved in an arrangement which effectively constitutes a container having a conductive screen at one end thereof, with opened apertures over the region of the pattern defining the character desired to be printed. Provision is made to replenish the pigment powder in the container by any suitable powder conveying means or by having the powder blown into the container under air pressure. The container may also, if desired, include carrier particles, such as small glass spheres, which are slightly larger than the apertures in the screen. The carrier particles assist in achieving uniform charging of the powder particles and also assist in providing a freer flowing mass of materials.

The container is supported to be movable to and from a printing position. At the printing position, spaced from the container, is a backplate which is conductive. If the material to be written on is sufficiently conductive to serve as an electrode then the backplate may be omitted. A source of potential is provided for establishing an electric field, between the screen and the backplate. Connection for establishing said field need not be made however, until the container is moved up to the printing position. Paper, or any other material to be Written on is interposed between the backplate and the container at the writing position. The container is rapidly carried from its rest position to the writing position, at which position its motion is abruptly stopped. At this position also, unless made all along, contact is made between the container and source of potential to establish the electrostatic field. As a result of the starting and stopping of the motion of the container, the carrier material therein, together with the powder in the container, are first carried backwards, away from the screen openings, and then by reason of the forces of inertia, are forced against the screen openings. Due to the forces of inertia the powder particles are thrust through the screen openings into the electric field whereby electrostatic printing is effectuated.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective sketch of the appearance of an embodiment of the invention;

FIGURE 2 shows a detail in perspective of an embodiment of the invention;

FIGURE 3 is a detail of one of the electrostatic writing elements employed in the embodiment of the invention;

FIGURE 3A is a detail of a filling arrangement which may be used in the embodiment of the invention;

FIGURE 4 shows another arrangement for the embodiment of the invention;

FIGURE 5 is a view in elevation of an embodiment of the invention used for printing on articles;

FIGURE 6 is a perspective view of containers used in FIGURE 5, and

FIGURE 7 is a side view of still another embodiment of the invention.

Referring now to FIGURE 1, there is shown the external appearance of one embodiment of the invention. It appears like an ordinary typewriter 10, having keys 12 and the arrangement is operated in exactly the same Way as a typewriter. [Paper is inserted into the carriage and the keys 1 2 may be actuated to print the character associated with the key.

In FIGURE 2 there is shown a detail of the typewriter indicating the improvements in accordance with this invention. Instead of having the standard type mounted on a bar, there is provided a small container 1 4, which as shown in an isometric view in FIGURE 3, may be cylindrical or square, as desired. This container is attached to a tube 16, which has a stop pin '18, mounted thereon. One face of the container 20, has a conductive screen with openings therein arranged in the form of the character 22, which is desired to be printed.

The container 14, the tube 16, and the stop bar 13, as well as the face 20, including the screen 22, are all conductive. Thus, when the stop pin 18, contacts a block bar 24, on the typewriter, which is connected to a potential source 26, the potential is applied to the entire container 14, including the front face 20. If desired, as shown in FIGURE 3, the entire container is nonconductive. The screen portion of the front face is conductiv'e. A conductor 19 extends from the stop bar 18 to the screen portion of the face. Paper 28 or any other writing material, is inserted into the carriage of the typewriter 10, and is guided by means of the roller arrangements 32, 34, in the usual manner, to be held opposite one of the electrostatic printing keys comprising the container 14 with the screen character in its front face, when the electrostatic printing key is at a printing position. Behind the paper 28, is a conductive metal backplate 36. The source of potential 26, is connected between the block bar 24, and the backplate 36. Therefore, when the electrostatic type 14 is brought up into the printing position shown in FIGURE 2, the source of potential 26 is connected between the back bar 36 and the screen 22, and the face 20, for establishing an electric field between the backplate and the printing face.

One of the electrostatic type heads 14, is shown in the operating position in FIGURE 2. It is brought to this position when an associated key 12A is depressed, closing the connection between two switch contacts 40A, 40B, whereby a circuit is made between a solenoid 42 and a source of exciting potential 45. When the solenoid is energized it pulls on its armature 44. The armature is pivotably attached to the rod 16. The rod is pivotably supported on a pivot 46. Accordingly, the solenoid can pull the electrostatic type from the address position shown, to the operating position shown at which printing may occur. The starting of the motion of the electrostatic type and the stopping by the contact of the stopping pin with the stop bar, are very abrupt.

As may be seen in FIGURE 3, the container 14 is filled with electrosoopic pigment powder particles 15. A carrier material, 17, such as glass beads, for example, may also be included. The pigment powder particles are sufficiently small to be able to pass through the apertures in the screen 22. The beads or spheres, are somewhat larger than these apertures. The container may be half filled with these glass balls 17, when they are used. The containers 14 are kept filled with a proper amount of powder by a powder reservoir 41, with which the containers 14 connect when they return to their rest positions. Each container has a projection 43, which extends from the top thereof. This projection is attached to a sliding door 45, which is biased by springs 47A, 47B, to close an opening 49 (see FIGURE 3A) in the top of the container when it is out of contact with the powder reservoir 40. When a container returns to its rest position the projection 43 strikes one of the tubes 51 extending from the reservoir, pushes it sufficiently -far to open the container. The container can then receive additional powder from the reservoir. The tubes 51 can each have a flap (not shown) which is moved to open the tube upon contact with the projection 43 to open the tube to permit a metered amount of powder to enter a container through the opening 4-9 therein.

The foregoing description of a mechanism for automatically refilling a container is by way of illustration only, and is not to be taken as a limitation upon the invention. Any suitable refilling arrangement may be used if desired without departing from the spirit and scope of this invention. As a practical matter, so little pigment powder is used on each writing transfer operation, that a considerable number of writing operations can occur before a powder refill is necessary. At this time a manual refill can be porformed through the opening 49 of the container.

When carrier material, such as the glass beads just described is used, an important function in the operation of the system is provided. As indicated initially herein, the powder will not, of its own volition, pass through the apertures of the screen into the electric field. The glass beads serve the function of pressing the powder through the screen particles into the field. Because of their inertia, when the key 12A is initially depressed, actuating the solenoid, these glass beads together with the powder in a container, are first thrown toward the back of the container. Then when the container is abruptly halted, the glass beads and the powder are thrown toward the front end of the container. The glass beads having a substantially greater mass than the powder particles, press these powder particles through the screen aperture into the electric field. The powder particles are carried by the electric field in the form of the pattern in which they are injected into that field toward the backplate 36. The paper 28 intercepts these powder particles. They remain adhered thereto, by reason of the electrostatic attraction between the powder particles and the paper. The powder particles can then be fixed on the paper either by heat, or by spraying, or other methods well known for fixing powder particles to a paper.

The use of the carrier particles is preferable for the foregoing reasons. However, there are some powders which have sufiicient mass and have ufficient flow, that upon the sudden start-stop of the container, they will pass through the screen into the electric field without requiring carrier particles. Thus, this invention is not to be limited to the use of carrier particles.

FIGURE 4 is a simplified schematic diagram showing how the embodiment of the invention may be employed in an arrangement akin to the high speed printing arrangements employed as a computer output printer. These arrangements usually have some mechanism for passing paper through a zone in which the printing occurs. The printing zone will have a plurality of lines of type which extend across the width of the paper. Each line of type will be identical, thus one line will have As, the next line Bs, etc. Each type character is solenoid actuated.

As the paper enters the zone of type it first passes the line of As. The computer provides signals indicating at which locations along the line the letter A should be printed. These signals are applied to the solenoids, which then print all the As on that line. As the line of type which has been printed, passes under the line of B type characters, the computer furnishes signals for actuating those solenoids which print Bs in the desired places. Thus, as the paper continues moving past each line of type, the computer actuates the solenoids for that line of type to effectuate, where necessary, the printing of the proper letter.

The present invention lends itself to this type of operation. This is shown in FIGURE 4. A backplate 52 is provided which extends over the entire printing zone for an electrostatic line printer. Each line of type will contain, by way of example, and not to be constructed as a limitation, only three electrostatic type heads, respectively 54A, 54B, 54C. One line is provided for each character desired to be printed. In order to simplify the showing, only two lines of type heads are shown. The type head, respectively 54A, 54B, 54C, will be substantially identical with the container 14 shown in FIG- URE 3. It will hold the pigment powder used in the actual printing process, plus when required, a substantial number of glass spheres.

For each line of type there is provided an arresting bar 56. A source of potential 58 is connected between the arresting bar and the backplate 52. The paper 61, passes between the backplate 52 and the electrostatic type heads 54A, 54B, 540. These type heads are at a resting position until a solenoid 60, a different one of which is associated with a different one of the type heads, is selectively actuated from a source of solenoid selecting signal-s 62. The solenoid 60 has an armature 64, which is attached to a supply tube 66. The supply tube has a stop pin 68, attached thereto. The supply tube is in communication with the electrostatic container.

Each one of the containers 54A, 54B, 54C, contains either powder alone or a mixture of powder and a carrier which may be substantially identical with the powder and carrier previously described. The supply of powder is maintained adequate by a mechanism which may include a powder reservoir 70, which is connected by means of a flexible tube 72, to the tube 66, an air compressor 74 supplies air so that the powder is blown through each one of the tubes 72 to each one of the chambers containing the powder. The tubes 66, may contain a valve, which opens when required, to admit both air and powder into the containers. Such valves may either be opened upon the return of the printing members by the solenoids 64, or any other suitable and Well known actuating mechanism.

The operation of the arrangement shown is as described. The electrostatic print members are selectively actuated by signals from the solenoid selector 62. They are stopped abruptly by the stop pin 68 coming in contact with the stop bar 56, whereby the carrier is thrown forward to force the triboelectric powder through the apertures of the screen in the electrostatic type head into the field. The powder adheres to the paper 61 and after the paper passes out from the printing station, the powder can be fixed in place by heat, a fixing spray, or any other well known mechanism for alfectuating the fixing of the powder to the paper.

FIGURES 5 and 6 illustrate another arrangement for electrostatic printing on objects such as bottles or cans, in accordance with this invention. It is preferred to print on bottles or cans while they are still hot, since in this manner the heat of the glass or metal fixes the pigment powder and thus an additional fixing step is eliminated.

By way of example, FIGURE 5 shows an arrangement for printing on glass bottles. The same arrangement may be employed for printing on cans. FIGURE 5 is a view in elevation of fragmented production of a line of bottles 80, 82, which are moved on a conveyor belt 86 through a printing station. As each bottle enters the printing station the carrying belt is stopped long enough to permit two reciprocal actuator motors respectively 88, 90, which are positioned on either side of a bottle in the printing station to reciprocally move two members respectively 92, 94, to close around the bottle and then return to their initial positions. The members 92, 94, are shown in their closed position. They are abruptly started toward one another and then are abruptly stopped by any such suitable mechanisms such as by bumpers 96, 98, carried by at least one of the members 94 for the purpose.

If printing is desired on only one side of the bottle then only one of the members 92 need be a container for pigment powder and/ or a carrier vehicle and the other need only be a backstop. If printing is desired on both sides of the bottle then both members 92, 94, can be containers. As shown in the perspective view in FIGURE 6, each container has a front face 100, which comprises a conduc tive screen having a masked portion 100M and an open screen portion 1005, which is in the form of the characters and/or design desired to be printed. The conductive screen may be shaped to fit the contours of the bottle, or can, on which printing is to occur.

Since hot glass is conductive and a can is usually made of a conductive metal, one method of establishing the electric field required to carry pigment powder over the distance (usually on the order of 0.025 in.) between the screen and the object to be printed on may be to use a conductive carrying belt 86, and connect a source of potential respectively 102, 104, between each printing container and the belt 86. The potential source may be left connected in at all times, since there is very little current drain on the power source. Alternatively, contacts re spectively 106, 108, may be carried by the containers to be closed and thus make the proper electrical connections to establish the required electric field when the containers 92, 94, are in the proper writing position relative to the bottle. Of course, a conductive path exists between the respective potential sources 102, 164, and the bottle 82, through the belt 86.

FIGURE 6, is a perspective view of the containers shown in FIGURE 5. The conductive screen 1% of one of the containers 92, may be seen having a masked portion M and an apertured portion 1008. It is preferred to reciprocally actuate the containers '92, 94, along a vertical axis, since with large size containers, gravity acts on the pigment particles to pile them up in the lower portion of the container. Thereby, the upper screen apertures do not receive the pigment particles. If the reciprocal actuation motion, where containers are moved horizontally, is made along a somewhat arcuate path, or if inside a container there is a rotating wheel to spread particles and carrier, or if a container is compartmentalized into many small containers behind the single front screen, then this difliculty, for larger size containers and for horizontal motion, is easily avoided.

The movement of the pigment particles alone, or pigment particles and carrier mixture is the same as has been described. Initially, these particles are thrown toward the rear of the container and then upon the sudden stop occurring, just short of touching bottle or can, the powder and carrier particles are thrown at the front screen with the result that powder particles pass through the screen [apertures directly into the electric field to be carried across to the bottle surface.

The containers may be large enough to contain enough pigment powder so that only an occasional filling is required, or any suitable known automatic refill arrange ment may be provided, such as has been described herein, which operates when the containers are in their retracted positions. The reciprocal operation of the actuator motors 88, 9%}, may be triggered when a bottle is in the printing position by any suitable sensing mechanism, such as the light source 116, and photoelectric detecting mechanism 118, shown in FIGURE 7. The bottle 121i interrupts the light source enabling the actuator motors to operate.

FIGURE 7 is a side view showing another arrangement for printing on a bottle or can. Here a reciprocal actuator motor arrangement 122, when triggered by a signal from the photoelectric detecting apparatus 118, suddenly starts the container 124 having a front screen 126, of the type described, toward the bottle 120. The contamer is stopped by the projection 128, which is carried thereon, striking a stop bar 130. This serves to connect the front screen, to a source of potential 132. The bottle rests on a conductive belt which is also connected either through a brush or other suitable contacting arrangement to the potential source 132. The pigment particles in the container are thrown through the screen at the moment of arrested motion toward the bottle, and enter the electric field, which is at that time established between screen and bottle, to be carried to and deposited on the bottle in a pattern defined by the openings of the screen.

As described above, the conveyor belt carrying the article to be printed on is stopped long enough to permit the writing operation to occur at the writing station. However, it is also possible to provide the reciprocal actuations of the containers actuated thereby with a motion which parallels that of the moving belt to enable the motion of the belt to continue uninterruptedly. The printing mechanism can travel a reciprocal path to return to its initial position to pick up the next can or bottle. A number of these printing mechanisms such as three, can be used spaced along a line so that each mechanism isresponsible for every third article. Or a number of printing mechanisms may be placed on a rotating device positioned adjacent a belt so that a new printing mechanism is provided for each article to be printed on.

The reciprocal actuator motor itself, if desired, can serve the function of starting the container in a direction toward the article to be printed on, stopping it, and then returning the container to its initial position. The stop bar then does not actually arrest the motion of the container but provides an electrical contact to connect the screen to the power source, if the screen is not already so connected. The reciprocal actuator motor can be a solenoid with a spring return, two oppositely operating and sequentially actuated solenoids, or a rotary motor with a bell crank arrangement to secure reciprocal operation.

Accordingly, there has been shown and described herein a novel, useful, and unique arrangement for effectuating on line electrostatic printing. It should be noted that the arrangement describe-d does provide a better print result than when brushes are used since the powder particles which are ejected into the electric field by this invention have no components of motion at an angle to the field, which does occur when .a brush is used to rub the triboelectric powder particles through the screen. For printing on articles having high temperatures at the time this arrangement enables the container to be in proximity of the heated article only long enough. to effectuate printing and then it is removed. Since this time is on the order of a few milliseconds, the container is removed from proximity to the hot article before its temperature is raised sumciently to have adverse effects.

I claim:

1. An electrostatic printing system for printing with electroscopic pigment powder particles on material comprising a container for said powder particles having an operating face including a region having the shape desired to be printed, a conductive screen covering said region and having a plurality of screen openings extending over said region, a conductive backing plate, means for positioning said material on which printing is to occur adjacent said backing plate, said pigment powder in said container having a particle size smaller than the openings of said conductive screen, a plurality of carrier particles in said container mixed with said pigment powder, the size of the carrier particles being larger than the size of the apertures of said screen, means for moving said container from a first position with its operating face at a distance from said material on which printing is to occur to a second position with its operating face close to said material, means for abruptly terminating the motion of said container at said second position, and means for applying a potential to said backing plate and said conductive screen at said second position to establish therebetween an electric field into which said particles of powder are introduced through the openings in said screen.

2. In an electrostatic printing system of the type wherein an article to be printed on with an electroscopic pigment powder is positioned in an electric field one of the electrodes of which is a conductive apertured screen having the shape of a character desired to be printed, the improvement comprising a movable container having said conductive apertured screen mounted in an operating face thereof, said pigment powder being in said container and having a particle size smaller than the openings of said screen, carrier particles in said container mixed with said pigment powder and having a particle size larger than the openings of said screen, means for moving said container with said apertured screen from a position away from said article toward said article when it is desired to print, and means for abruptly terminating the motion of said container at the desired position for printing.

3. A system for electrostatic printing with an electroscopic pigment powder comprising a plurality of electrostatic printing members, each printing member including a conductive container having an operating face, said operating face including a foraminous region having the shape of a character desired to be printed, said pigment powder being in said container and having a particle size smaller than the openings of said foraminous region, means for selectively moving an electrostatic printing member to a predetermined printing position at which printing is to occur, means for abruptly terminating the motion of said electrostatic printing member at said predetermined printing position, mcans including said printing member for establishing an electric field at said predetermined printing position, and carrier particles in the container of said printing member having a particle size larger than the openings of said foraminous region, said carrier particles being mixed with said powder particles for pushing said pigment powder through the openings in the foraminous region of said printing member upon the abrupt termination of motion of said electrostatic printing member at said predetermined printing position,

4. An electrostatic printing system for printing with electroscopic powder particles comprising a plurality of electrostatic printing members, a conductive backing plate, means for selectively bringing a printing member to a predetermined printing position opposite said conductive backing plate, means for abruptly terminating the motion of said printing member at said printing position, means for establishing an electric field between said conductive backing plate and said printing member at said printing position, each said printing member including a container having a front face, a foraminous region in said front face describing the pattern of a character desired to be printed, said powder particles being in said container and having a particle size smaller than the apertures in said foraminous region, and means for pushing said powder through said apertures of said foraminous region at said predetermined printing position including a plurality of carrier particles mixed with said powder particles and having a particle size larger than the apertures of said foraminous region.

5. Apparatus for printing electrostatically on an article with electroscopic pigment particles comprising a container having a front face including a conductive screen with masked regions and apertured regions, said apertured regions having a pattern desired to be printed on said article said pigment powder particles being in said container and having a particle size which is smaller than an aperture of said screen, a plurality of carrier particles mixed with said pigment powder each particle of which is larger than an aperture of said screen, means for reciprocally moving said container from a position removed from said article to a position with said conductive screen adjacent said article with sufiicient abruptness to cause said pigment powder to move through said screen apertures, and means for establishing an electric field including said article and said conductive screen at the position of said container when said conductive screen is adjacent said article.

References Cited by the Examiner UNITED STATES PATENTS 2,618,551 11/1952 Walkup.

2,716,048 8/1955 Young.

2,930,351 3/1960 Giaimo 118-637 3,008,826 11/1961 Mott et al.

3,081,698 3/1963 Childress et al.

FOREIGN PATENTS 780,935 8/1957 Great Britain.

ROBERT E. PULFREY, Primary Examiner. DAVID KLEIN, WILLIAM B. PENN, Examiners. 

2. IN AN ELECTROSTATIC PRINTING SYSTEM OF THE TYPE WHEREIN AN ARTICLE TO BE PRINTED ON WITH AN ELECTROSCOPIC PIGMENT POWDER IS POSITIONED IN AN ELECTRIC FIELD ONE OF THE ELECTRODES OF WHICH IS A CONDUCTIVE APERTURED SCREEN HAVING THE SHAPE OF A CHARACTER DESIRED TO BE PRINTED, THE IMPROVEMENT COMPRISING A MOVABLE CONTAINER HAVING SAID CONDUCTIVE APERTURED SCREEN MOUNTED IN AN OPERATING FACE THEREOF, SAID PIGMENT POWDER BEING IN SAID CONTAINER AND HAVING A PARTICLE SIZE SMALLER THAN THE OPENINGS OF SAID SCREEN, CARRIER PARTICLES IN SAID CONTAINER MIXED WITH SAID PIGMENT POWDER AND HAVING A PARTICLE SIZE LARGE THAN THE OPENINGS OF SAID SCREEN, MEANS FOR MOVING SAID CONTAINER WITH SAID APERTURED SCREEN FROM A POSITION AWAY FROM SAID ARTICLE TOWARD SAID ARTICLE WHEN IT IS DESIRED TO PRINT, AND MEANS FOR ABRUPTLY TERMINATING THE MOTION OF SAID CONTAINER AT THE DESIRED POSITION FOR PRINTING. 